1. Field of the Invention
The present invention relates to a chemically amplified resist composition and a process for the formation of resist patterns using the same. More particularly, in one aspect, the present invention relates to a resist composition which can be exposed to any patterning radiation having a relatively short wavelength such as excimer laser light and can also utilize an alkaline solution as a developer. The chemically amplified resist composition of the present invention can provide fine positive-working resist patterns without swelling. Further, the thus produced resist patterns can provide a practically usable sensitivity and an excellent resistance to dry etching. In another aspect, the present invention relates to a resist composition which can exhibit a higher resolution, higher sensitivity and excellent resistance to dry etching, and also can effectively avoid cracking in the resulting resist patterns and peeling-off of the patterns from the substrate. Accordingly, the present invention can be advantageously utilized in the production of semiconductor devices such as semiconductor integrated circuits, for example, LSIs, VLSIS, ULSIs and other devices, using a lithographic process.
2. Description of the Related Art
Recently, in the production of semiconductor integrated circuits, the degree of integration thereof has been notably increased and accordingly LSIs and VLSIs have been produced on a commercial scale. The minimum line width of the circuit patterns in these devices approaches the sub-half micron or quarter micron order. In other words, in the production of these high performance devices, it is required to provide an established fine fabrication technology.
In the field of lithography, to satisfy the above requirements, an approach in which ultraviolet (UV) radiation as an exposure source is shifted to shorter wavelengths in the far or deep ultraviolet region has been suggested, along with research for providing new exposure devices provided with a light source capable of emitting such short wavelength radiation in the deep ultraviolet region.
Currently, photolithograpy using a krypton fluoride (KrF) excimer laser having a wavelength of 248 nm as an exposure source has been noted as a novel exposure technology, and it has also been urged to find novel resist materials suitable for exposure to such short wavelength radiation and stably showing a high sensitivity and high resolution. A chemical amplification system and a resist material based on said system, i.e., chemically amplified resist composition, have been disclosed by Ito et al. of IBM Corp. to be useful for KrF lithography (see, for example, J. M. Frechet et al., Proc. Microcircuit Eng., 260 (1982); H. Ito et al., Digest of Technical Papers of 1982 Symposium on VLSI Technology, 86 (1983); H. Ito et al., "Polymers in Electronics", ACS Symposium Series 242, edited by T. Davidson, ACS 11 (1984); and U.S. Pat. No. 4,491,628). As will be easily understood by referring to these articles, the basic concept of the chemically amplified resist composition developed by Ito et al. resides in that a catalytic reaction is first induced in the coating from the resist composition, thereby increasing an apparent quantum yield to a level sufficient to highly increase a sensitivity of the resist composition.
The above concept of the chemically amplified resist composition will be further clarified with reference to one typical example of the well-known chemically amplified resist compositions which have been widely studied by the researchers in the field of resist chemistry, namely, the chemically amplified resist composition comprising t-buthoxycarbonyl polyvinylphenol (t-BOCPVP) and a photoacid generator (PAG) capable of releasing an acid upon action of the exposure radiation. After it was coated over the substrate, the resist composition is exposed to the exposure radiation, and as a result of such exposure, an acid is released from the PAG. Then, the exposed resist composition or coating is subjected to post-exposure baking (PEB). As a result of this baking, in the exposed areas of the resist coating, a t-BOC group is cleaved from t-BOCPVP to produce isobutene and carbon dioxide. Further, a protonic acid simultaneously produced during cleavage of the t-BOC group can act as a catalyst in the above-mentioned cleavage reaction which therefore proceeds like a chain reaction, thus largely varying the polarity of the exposed areas. In this resist composition, if a suitable developer which is compatible with such a large variation of the polarity in the exposed areas is selected, satisfactory resist patterns can be easily produced.
However, conventional chemically amplified resist materials including the above-discussed t-BOCPVP-based resist composition have one problem in that because of the restricted chemical structure of the resin used as a basic component thereof, they cannot fully satisfy the requirements concerning sensitivity, transparency to the exposure radiation, stability in storage, ease in procurement, resolution and the like. Among the possible restrictions to the chemical structure of the resist resin, the most important restriction is the restriction to a protective group which is attached to said resin, but is able to be cleaved therefrom upon baking of the exposed resin in the presence of a photoacid generator. Namely, in the film-forming resin in which a side chain of the monomeric unit of the resin contains a carboxylic acid ester attached thereto as a chemical amplification-concerning component, protective groups which are recognized to be suitable for the carboxyl group of said ester include only t-butyl group, 1,1-dimethylbenzyl group, tetrahydropyranyl group, 3-oxocyclohexyl group and isobornyl group. These protective groups are inappropriate, and therefore it is desired to provide a new protective group which can be more effectively utilized in the chemically amplified resist materials than the above protective groups.
In addition to the improvement in the protective group introduced into the resist resin, the conventional fine fabrication technology includes problems concerning some defects in the resulting resist patterns which defects will be described hereinafter.
Using the fine fabrication technology, fine resist patterns can be generally produced by coating a substrate having on a surface thereof a layer or coating to be fabricated, such as a layer to be selectively etched, with a resist material, and exposing the resist coating to a patterning radiation to thereby form a latent image corresponding to a pattern of said radiation. The latent image of the resist coating is then developed with a suitable developer. A desired resist pattern is thus obtained. The resist pattern can be effectively utilized as a masking means in the subsequent etching process to selectively etch the underlying layer. Said patterning radiation generally includes ultraviolet radiation such as the g-line (wavelength of 436 nm) and i-line (wavelength of 365 nm), however, as briefly mentioned in the above paragraphs, it also includes other radiations having shorter wavelengths such as deep ultraviolet radiation, vacuum ultraviolet radiation, electron beam (EB), X-ray and others as well as excimer laser such as KrF laser of the wavelength of 248 nm and ArF laser of the wavelength of 193 nm. Note that the term "radiation" used herein means all of the above-mentioned radiations.
In the formation of submicron-ordered resist patterns using as a patterning radiation the radiation in the range of far ultraviolet or vacuum ultraviolet regions, it is necessary to use specific resist materials having an excellent transparency to the patterning radiation and also a high resistance to dry etching. The inventors of this application have zealously studied this and found that said need is satisfied by the radiation-sensitive material comprising a polymer or copolymer of acrylic acid ester or a-substituted acrylic acid ester in which the ester portion contains an adamantyl skeleton (see, Japanese Unexamined Patent Publication (Kokai) No. 4-39665). Similarly, the inventors have found that the chemically amplified radiation-sensitive material comprising a polymer or copolymer of acrylic acid ester or .alpha.-substituted acrylic acid ester in which the ester portion contains a norbornane skeleton (see, Japanese Unexamined Patent Publication (Kokai) No. 5-257284).
Surprisingly, the chemically amplified resist materials suggested by the inventors have an excellent resistance to dry etching, in addition to a higher transparency to radiation from wide variety of light sources, especially excimer laser light having a wavelength in the far ultraviolet and vacuum ultraviolet regions. However, these resist materials still have drawbacks concerning difficulty in obtaining stable patterning characteristics. For example, depending upon the conditions applied to the materials, for example, when they are coated at a relatively larger thickness or the exposed resist coating is developed with a developer having a higher solubility, the resist materials are liable to cause cracking of the resist patterns or separation or peeling off of the patterns from the underlying layer. The exact reason why such defective resist patterns are produced is unknown, however, the inventors of the present application understand from their experience that since alicyclic hydrocarbon moiety in the skeleton of the resist material has a strong hydrophobic nature and rigidity, the strain applied to the resist coating during development is increased.
Further, due to presence of the alicyclic hydrocarbon moiety therein, the above-mentioned chemically amplified resist materials suffer from the drawback that conventional alkaline developers cannot be used in the development process. Namely, it is understood that due to a strong hydrophobic nature of the alicyclic hydrocarbon moiety, the resist materials containing said alicyclic moiety cannot be sufficiently dissolved in the alkaline developers. Note, however, that the inventors have found that the above problem concerning use of the alkaline developers can be solved if the formation of resist patterns is made by using a resist material which comprises a polymer or copolymer having a repeating unit containing a protected alkali-soluble group capable of releasing a protective group upon exposure to an acid, thereby making the polymer or copolymer alkali-soluble, and a photoacid generator capable of producing an acid upon exposure to radiation, and developing the exposed resist coating with a developer containing an aqueous solution or alcoholic solution of the specified ammonium compound or morpholine compound (see, Japanese Patent Application No. 7-23053 filed on Feb. 10, 1995).
Furthermore, other problems in the above-mentioned chemically amplified resist materials are that due to its poor adhesion to the underlying layer or coating to be etched, the resist coating can separate from the substrate during development, and that when the patterning exposure of the resist coating is made through an exposure mask which is designed to prevent permeation of the patterning radiation corresponding the circuit pattern to be printed, the resulting resist patterns have an expanded configuration larger than that of the exposure mask used. It is therefore desired to provide a resist material capable of exactly and faithfully reproducing the fine patterns of the exposure mask used.